Aptitude GPG Error Simple Solution

Always getting some gpg error while trying to do aptitude update on older version of debian platform such as etch or lenny. The message looks like this :

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA

what should we do?
1st of all you have to be a root and check the key first with pgp.net server : the command is :
#gpg --keyserver wwwkeys.us.pgp.net --recv-keys AED4B06F473041FA

then it should return like this :

gpg: requesting key 473041FA from hkp server wwwkeys.us.pgp.net
gpg: key 473041FA: public key "Debian Archive Automatic Signing Key (6.0/squeeze " imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)



what's next?


#gpg --armor --export | apt-key add -


then do aptitude update again and it should work